A phenomenon in which the temperature of an urban area becomes higher than the temperatures of the surrounding areas is called “heat island phenomenon.”
In recent years, the heat island phenomenon in cities has been said to be a cause of worsening urban environments in conjunction with the influences of global warming. It is said that in the last 100 years, the global average temperature has risen by 0.6° C., while in Japan the temperatures in large cities have risen by 2.4° C., and the temperature in Tokyo has risen by 2.9° C.
The heat island does not necessarily refer to only a high-temperature area confined exclusively to city blocks. For example, it is known that, on a summer afternoon, a vast heat island is formed extending from adjacent areas of Tokyo to inland areas of the Kanto Plain. A temperature rise on the scale of the inland area may directly affect meteorological changes, and hence there has been an increasing demand for meteorological prediction that takes into account influences not only from the atmosphere but also from adjacent areas of the heat island and adjacent sea thereof.
In recent years, regarding such concentrated torrential rainfalls as urban concentrated torrential rainfalls, for which the heat island is considered to be one of the causes, there is known the fact that a convergence field of wide-area winds blowing from inland areas surrounding the heat island and from adjacent sea thereof has a significant influence on the distribution of the rainfall and the amount thereof.
In order to clarify the mechanisms of such phenomena that may directly result in disasters and to make predictions thereon, it is necessary to provide such a simulation model that is capable of establishing direct cause-effect relations between meso-scale meteorological phenomena and environments typical of cities, that is, decrease in sky factor, distribution of shadows caused by buildings, radiation from the buildings and reflection thereof, heat storage effect of walls and roads, decline in wind speed among the buildings, and the like, which are regarded as factors characterizing the heat island.
Conventionally, many numerical urban simulations have used anyone of a model in which a building space in a city is represented by a slab model and a model in which the building space is represented by a canopy model.
In the slab model, it is difficult to express complex changes in heat balance in the building space, and there is a tendency to overestimate heating in city areas during daytime.
In the canopy model, urban surfaces are treated as street canyons, and hence it is possible to take into account the factors characterizing the building space in the city (urban canopy), such as the sky factor, the shadow factor, the reflection of radiation, the heat storage effect of the walls, and decline in wind speed within the canopy. However, the canopy model is based on the assumption that the buildings within the urban canopy are arranged in a regular manner. Accordingly, the sky factor, the shadow factor, the reflection of radiation, the heat storage effect of the walls, the decline in wind speed within the canopy, and the like are insufficient for reproducing or making a prediction on heat retention, heat storage, and the like for an ideal condition, that is, uniform arrangement of identically-shaped buildings.
Non-patent Document 1: Kazuya Harayama, Ryozo Ooka, Shuzo Murakami, Shinji Yoshida, Masahiro Setojima, Hiroaki Kondo: “STUDY ON URBAN CLIMATE ANALYSIS BASED ON MESO-SCALE CLIMATE MODEL INCORPORATED WITH THE URBAN CANOPY MODEL”, Journal of Environmental Engineering, Architectural Institute of Japan, 2005, No. 592, pp. 75-82.
Non-patent Document 2: Fumiaki Fujibe: “THE URBAN HEAT ISLAND”, Tenki, 2007, No. 54(1), pp. 9-12.
Non-patent Document 3: Hong Chen, Ryozo Ooka, Hong Huang, Madoka Nakashima: “STUDY ON IMPACT OF BUILDINGS ON OUTDOOR THERMAL ENVIRONMENT USING COUPLED SIMULATION OF CONVECTION, RADIATION AND CONDUCTION”, Proceedings of the 19th Symposium on Computational Fluid Dynamics, 2005, C1-3.
Non-patent Document 4: Taiki Sato, Shuzo Murakami, Ryozo Ooka, Yoichi Kawamoto: “ESTIMATION OF STANDARD EFFECTIVE TEMPERATURE (SET) AT THE PEDESTRIAN AREA BASED ON NUMERICAL CLIMATE MODEL”, Summaries of Technical Papers of Annual Convention, Architectural Institute of Japan, 2005.
Non-patent Document 5: Aya Hagishima, Jun Tanimoto, Tadahisa Katayama, Kenji Ohara: “AN ORGANIC ANALYSIS FOR QUANTITATIVE ESTIMATION OF HEAT ISLAND BY THE REVISED ARCHITECTURE-URBAN-SOIL-SIMULTANEOUS SIMULATION MODEL (AUSSSM): PART 1 THEORETICAL FRAME OF THE MODEL AND RESULTS OF STANDARD SOLUTION”, Journal of Architecture, Planning and Environmental Engineering, Architectural Institute of Japan, 2001, No. 550, pp. 79-86.
Non-patent Document 6: Aya Hagishima, Jun Tanimoto, Tadahisa Katayama, Kenji Ohara: “AN ORGANIC ANALYSIS FOR QUANTITATIVE ESTIMATION OF HEAT ISLAND BY THE REVISED ARCHITECTURE-URBAN-SOIL-SIMULTANEOUS SIMULATION MODEL (AUSSSM): PART 2 QUANTITATIVE ANALYSIS BASED ON A SERIES OF NUMERICAL EXPERIMENTS”, Journal of Architecture, Planning and Environmental Engineering, Architectural Institute of Japan, 2002, No. 553, pp. 91-98.
Non-patent Document 7: Aya Hagishima, Jun Tanimoto, Fumihiro Asano: “AN ORGANIC ANALYSIS FOR QUANTITATIVE ESTIMATION OF HEAT ISLAND BY THE REVISED ARCHITECTURE-URBAN-SOIL-SIMULTANEOUS SIMULATION MODEL (AUSSSM): PART 3 SENSITIVITY ANALYSIS ON FACTORS OF URBAN HEAT ISLAND UNDER VARIOUS METEOROLOGICAL REGIONS”, Journal of Environmental Engineering, Architectural Institute of Japan, 2006, No. 601, pp. 43-50.
Non-patent Document 8: Hiroyuki Kusaka, Fujio Kimura: “MECHANISM FOR NOCTURNAL HOT AND HUMID CONDITIONS USING A WEATHER MODEL”, Tenki, 2004, No. 51(2), pp. 95-98.